USB ports and cables allow interconnection of a variety of compatible electronic devices, such as desktop computers, automobile dashboard consoles and battery-powered portable devices such as laptop computers, tablets, mobile phones, e-readers and MP3 players. USB ports are accessed using standardized USB cable connections to provide serial communications between devices, as well as electrical power transfer for charging and operating battery-powered peripheral devices. USB compatible systems often include interface integrated circuits (ICs) mounted to an internal host circuit board to interface USB data and power connections to host system circuitry such as power circuits and host processors. Dedicated USB charging devices are also available having multiple USB ports for charging various portable devices, which may include circuitry for fast charging certain peripheral devices. Many desktop and laptop computers include multiple USB ports for data transfer and/or peripheral device charging.
USB power delivery (USB-PD) and Type-C (USB-C) specifications describe delivery of higher power over USB cables and connectors to provide a universal power plug for devices that may accommodate more than 5V charging power, for example, for fast or quick-charging capabilities. The USB-PD specification defines communications for negotiating voltage and current levels for power transfer from a source port to a sink port, where the power negotiation communications is independent from the normal USB communications. USB-PD defines four kinds of USB compatible devices: Provider-Only, Provider/Consumer, Consumer/Provider, and Consumer-Only. Devices that are Provider-Only, Provider/Consumer, or Consumer/Providers may sometimes be in a Source role providing DC voltage on the VBUS wire or line for the far-end device to consume or sink. USB-C recognizes three kinds of USB devices, including a downward facing port (DFP), an upward facing port (UFP), and a dual-role port (DRP). In the absence of USB PD messaging, the DFP is the source of power and the UFP is sinking the power.
USB-C cables and connectors include configuration channel (CC) lines for power configuration as well as for baseband communications. USB-PD specifications provide baseband communications using Biphase Mark Coding (BMC) for message exchange over a configuration channel (CC) wire or line of the USB cable. USB-C systems use a Type-C plug with two configuration channel lines CC1 and CC2. The USB-PD specification defines a half-duplex packet-based communication link between ports connected via a USB-PD cable and connectors to exchange information that enables the two ports to communicate and negotiate the voltage and current provided from a Source port to a Sink port. The ports can negotiate to switch roles (Source to Sink and vice versa). The BMC communications on the CC lines is independent from the normal USB communications that go through D+ and D− lines of the USB cable. The CC line or lines may also be used for negotiating power transfer configurations of connected devices by way of analog signal levels. For example, up to 15 W of power can be delivered for USB Type-C cables without USB-PD messaging by controlling the DC voltage on the CC pin.
In addition, USB Type-C cables include sideband usage or SBU lines, and USB Type-C cables are powered cables facilitating multiple functionality between USB compatible devices. For instance, the SBU lines can be used for audio left and right signals. As a result of the large number of configurable functions implemented using USB Type-C interconnections, a variety of different voltage levels can be present on adjacent lines within a USB Type-C cable. As a result, short-circuits or other failures between adjacent USB Type-C cable lines can lead to overvoltage conditions which can cause stress or failure of a host circuit. For example, the nominal voltage of the CC line is determined by pull up current from the DFP device (e.g., using a pull up resistor RP or a current source) and a pull down resistor RD (or pull down current source) from the UFP device, and the CC line voltage in this configuration can vary from 0.3V to 2.4V due to combinations of the pull up and pull down levels. In addition, the baseband communication signals on the CC lines for typical BMC data packet exchange range from 0 to 1.1V. In contrast, voltages on other USB Type-C cable lines can be 5 V or other voltage levels above the normal operating range for the CC lines. In this regard, USB Type-C cables and cable plugs locate the SBU lines, the data lines D+ and D− and the CC lines adjacent or near each other, and close to the VBUS lines. A short circuit between a data or SBU line and one of the adjacent lines can therefore create an overvoltage condition.